1. Field of the Invention
This invention relates to a method for manufacturing a copper-containing oxide superconducting thin-film on the surface of a substrate, by use of a sputtering method.
2. Description of the Related Art
Nowadays, considerable attention is being paid to an oxide superconductor as a potential high-temperature superconductor This situation has come about as a result of the discovery that a Ba-La-Cu-O type layered perovskite oxide has a high critical temperature Tc. Thereafter, it was shown, in Phys, Rev. Lett. vol. 58. No. 9 pp908 to 910, that an oxygen-deficient perovskite oxide superconductor represented by YBa.sub.2 Cu.sub.3 O.sub.7-.delta. has a critical temperature Tc of over 90 K. Since the time of these discoveries, emphasis has been placed on the development of a technique of application of the oxide superconductor. Since, in the field of microelectronics, much consideration has been given to the application of an oxide superconductor to a SQUID (superconducting quantum interference device), HEMT (high electron mobility transistor) interconnection wirings, etc., the thin-film technique is judged to be an essential requisite in the application thereto of the oxide superconductor.
A sputtering operation in an inert gas atmosphere is often performed in the process for forming a thin film of an oxide superconductor. This type of sputtering operation has also been used in the formation of a thin film of YBa.sub.2 Cu.sub.3 O.sub.7-.delta., for which reference is invited to Jap. J. Appl. Phys. 26 (1987) L709-710, May 20; H. Adachi et al.
However, when a YBa.sub.2 Cu.sub.3 O.sub.7-.delta. thin-film is formed within an inert gas atmosphere, the following problem occurs. That is, if a heat treatment is performed on the thin film in order to obtain a high critical temperature, the critical temperature value varies and is unsatisfactory in some cases. A bulk formed of the oxide superconductor of the afore-mentioned composition will have a relatively stable critical temperature Tc if it is heat treated. A thin film of the same oxide superconductor cannot have a sufficiently stable critical temperature Tc, since it is difficult to heat-treat the thin-film appropriately. As a result, the critical temperature Tc of the thin-film is lower than that of the bulk.
Jap. J. Appln. Phys. 26 (1987) L738 to L740, May 20; M. Kawasaki et al reports a case where, upon the formation of a YBa.sub.2 Cu.sub.3 O.sub.7-.delta. thin-film, sputtering is performed within a mixed inert gas/10 to 20% oxygen gas atmosphere, to allow an easy sputtering operation. Using this technique, it is still difficult to obtain a high critical temperature stably.